An electrical fault which shut down immigration control systems at Birmingham Airport caused delays for hundreds of passengers.
Passport checks were affected by the shutdown and UK Border Agency staff had to resort to manual checking.
Eyewitnesses claimed a number of people walked through passport control before manual checks were initiated.
On Thursday evening the Home Office confirmed IT systems were working again.
John Shotton, from Shrewsbury, who arrived from Alicante, said about 1,000 people had been held at the airport while staff checked passports manually.
He said some passengers had been waiting more than three hours.
A UK Border Agency spokesman said the priority was to “maintain the security of the UK border at all times” and apologised for the delays caused by the manual checks.
The problems did not affect outgoing flights.
BBC © 2012